The invention relates to a composite material made of a coated hard metal or cermet substrate in which the sole layer or at least one layer of a multiple layer coating with a thickness of 0.5 xcexcm to 25 xcexcm, preferably the outermost layer, contains an Al2O3xe2x80x94phase and a phase consisting of ZrO2 and/or HfO2.
The invention relates further to a method of producing a layer containing a Al2O3 phase and a phase consisting of ZrO2 and/or HfO2 on a substrate or substrate body coated with one or more layers by means of a CVD (Chemical Vapor Deposition) process at deposition temperatures ranging between 900xc2x0 C. and 1000xc2x0 C. in the gas phase which contains the gases necessary for the deposition and selected from the Group AlCl3, ZrCl4, HfCl4, CO2, H2, CH4 and N2 or inert gases, and under pressures of 10 to 100,000 Pa.
DE 27 36 982 A1 already describes a wear-resistant layer for preformed parts, particularly tools, consisting of a formed body, preferably of hard metal, and one or more surface coatings, of which at least one protective layer consists of a ceramic matrix in which a further material has been embedded. The ceramic matrix and the embedded material have clearly different heat expansion coefficients, so that the protective layer is pervaded by extremely fine microcracks. As an embedding material in a ceramic matrix of Al2O3 a destabilized and/or partially stabilized ZrO2 is provided. For the production of such a layer by the CVD process, aluminum trichloride, carbon dioxide and hydrogen for the formation of Al2O3 are introduced in the gas phase together with zirconium tetrachloride and water vapor for the formation of ZrO2, in a reactor at 1100xc2x0 C. Due to the density difference between zirconium oxide which is tetragonal above a conversion temperature of 1100xc2x0 C. and monoclinal below approximately 1100xc2x0 C., in a corresponding phase conversion a considerable volume modification of the embedded zirconium oxide results. As a consequence, with the increasing percent by volume of the zirconium oxide, the microcrack density in the deposited ceramic layer is increased.
DE 28 25 009 C2 describes a hard metal body with a thin wear-resistant surface layer of aluminum oxide, which consists entirely or at least 85% of xcexa modification and that a balance consisting optionally of the xcex1-modification is created on the surface areas, e.g. in spots with a size of maximum 10 xcexcm. In addition, the aluminum oxide layer can contain additions of titanium, zirconium and/or hafnium. For the production of this ceramic layer by means of the CVD process, besides H2, AlCl3, CO2 and CO and also minimal amounts of 0.03 to 0.5% TiCl4 are added to the gas mixture.
This addition, however, serves exclusively or almost exclusively for the formation of the xcexa-aluminum-oxide phase.
A further CVD process for the deposition of Al2O3 and/or ZrO2 by using an additional reagent, such as hydrogen sulfide is described in EP 0 523 021 B1.
DE 195 18 927 A1 describes a coated cutting tool with a sintered carbide or ceramic substrate, with a wear-resistant compound ceramic coating, which has two different metal oxide phases, e.g. Al2O3 and ZrO2, as well as a doping agent selected from the group which consists of sulfur, selenium, tellurium, phosphorus, arsenic, antimony, bismuth or compounds of the mentioned elements. For the production of this two-phase layer according to CVD process, for instance aluminum and zirconium chloride, carbon dioxide with hydrogen as carrier in addition to a H2S gas are guided over the substrate body at a temperature of approximately 700 to 1250xc2x0 C. and a pressure of 113 Pa to atmospheric pressure, whereby a two-phase layer is deposited with the doping agent.
It is the object of the present invention to improve the wear resistance of the composite material mentioned at the outset.
It is another object to provide a composite material which can be used as a cutting insert in machining operations with improved tool life and efficiency.
Further it is the object of the present invention to provide a method for the production of the improved composite material.
These objects as achieved with the composite material of the invention which is characterized in that in the layer containing Al2O3 and ZrO2, HfO2 or mixtures thereof, a third finely dispersed phase is embedded, which consists of an oxide, oxycarbide, oxynitride or oxycarbonitride of titanium. Particularly the third phase can consist of TiO2, TiO, Ti2O, Ti2O3, Ti(O, C), Ti(O, N) or Ti (O, C, N) or mixed phases thereof, which in the following are generally referred to as TiOx phases. The embedding of the TiOx compounds in the two-phase ceramic layer will advantageously cause a dispersion-enhancing effect in the two-phase ceramic layer, which will considerably improve the wear resistance of this layer.
The hard metal or cermet substrate has a coating of one or more layers of a thickness of 0.5 to 25 xcexcm with the sole layer or at least one layer, preferably the outermost layer having the third phase.